1. Field of the Invention
The present invention relates to a hydrophilic surface treating aqueous solution, hydrophilic surface treating method and hydrophilic surface treating film, and more particularly, to a hydrophilic surface treating aqueous solution, hydrophilic surface treating method and hydrophilic surface treating film, capable of forming a film having anticorrosion and hydrophilicity on aluminum material such as aluminum fins of a heat exchanger.
2. Description of the Related Arts
Aluminum and its alloys are widely utilized for heat exchangers due to their light-weight and superior processability and thermal conductivity. With the spread of air conditioning systems, the number of cooling equipment or dehumidifying/cooling/heating air-conditioners is increasing. Typically, fins made of aluminum alloy are provided on the heat exchanging sections of these air-conditioners.
During the cooling mode of the air-conditioners, in general, the moisture in the air tends to adhere to the surface of the fins in the form of condensed water. It is therefore conceivable to confer a water repellency on the fin surface. The fin surface having the water repellency properties may allow the adhesion of the condensed water onto the fins in the form of hemispheres and the presence of bridge-like water between the fins. This will disadvantageously prevent the air flow of the heat exchanger and increase the air conducting resistance. Thus, the repellent fin surface may contribute to the reduction in heat exchanging efficiency.
Aluminum and its alloys originally have a good anticorrosion. In the case where the condensed water remains on the fin surface for a long period of time, a hydration reaction or corrosion reaction are accelerated due to the formation of an oxygen concentration cell on the fin surface and to the adhesion and condensation of contamination components in air. Thus, the corrosion products which have been produced by the above reaction accumulate on the fin surface, which will impair the heat exchange ability and during the heating, drive in winter cause the exhaust of white minute powder particles from the air fan together with the warmed air.
In order to solve the above problems, it has thus become desirable in recent years to improve the hydrophilicity and anticorrosion on the fin surface.
For example, U.S. Pat. No. 4,973,359 titled "Surface Treatment Chemical and Bath for Forming Hydrophilic and Coating and Method of Surface Treating Aluminum Members" discloses a hydrophilic surface treating chemical, and so on, which contains predetermined amounts of the sodium salt and/or potassium salt of carboxymethyl cellulose, ammonium salt of carboxymethyl cellulose, and N-methylol acrylamide.
Moreover, Japanese Patent Laid-open Publication No. 4-316,837 titled "Coated Aluminum Material and Method of Manufacturing the Same" discloses a coated aluminum material consisting of (a) 100 parts by weight of aqueous organic resin and (b) 50 to 1,200 parts by weight of nonionic surfactant, and having a hydrophilic film of 0.05 to 5 .mu.m. As the aqueous organic resin, listed are aqueous acrylic resin, polyester resin, epoxy resin, alkyd resin, and polyvinyl alcohol resin. It says that an alkylallylether-type nonionic surfactant is preferable as the nonionic surfactant.
However, the hydrophilic surface treating chemical disclosed in the above U.S. Pat. No. 4,973,359 exhibited a poor moldability of the aluminum material subjected to the above hydrophilic surface treating chemical, in a so-called precoat treatment in which the aluminum material is processed into a heat exchanger after the hydrophilic treatment of the aluminum material, irrespective of its satisfactory die friction and odor. Also, the application of a lubricant onto the treating film formed by use of the hydrophilic surface treating chemical did not fully improve the moldability. Furthermore, the repetition of the warming and immersion in flowing water resulted in the deterioration of hydrophilic surface treating film and presented insufficient persistency of the hydrophilicity.
The hydrophilic film described in Japanese Patent Laid-open Publication No. 4-316,837 provides good hydrophilicity and pressing processability in cooperation with the volatile lubricating oil. In this case, however, after the application and baking of the hydrophilic film of the gazette onto the aluminum material, the volatile lubricating oil had to be further applied and baked. In other words, double-coating is required to obtain a desired performance, which will result in poor productivity. A polyoxyalkylene surfactant is also disclosed as a nonionic surfactant, which is quite different in molecular weight and performance from the present invention.